Reduced-angle mammography device and variants

ABSTRACT

The invention relates to the mammography devices based on registration of a reduced-angle coherently scattered radiation when an object is rayed by a penetrating radiation. Registration of the radiation coherently scattered by an object allows to produce an image of an object in the form of distribution of its structural characteristics. The device comprises a system for forming a directed on a tested object, narrow small-divergence beams, or a beam, having the same characteristics, and a system for extracting the radiation that is coherently scattered in small angles by an object. The invention proposes versions of a device that also provide for registration of the radiation passed through an object to make allowance for its thickness so that to obviate the necessity to compress the breast. The device allows to carry out relative movements of an object and system of irradiation-registration, as well as irradiate an object at different angles and by a number of radiation sources simultaneously. The possibility to register the coherently scattered radiation in ultra-small angles within the range of several angular seconds to 0.5 degree, and also the possibility to form the primary radiation beam having a sharp boundary are provided as well.

FIELD OF THE INVENTION

The proposed invention relates to devices for producing an object imageusing reduced-angle scattering of a penetrating radiation, namely—tomammography devices that determine changes in the tissue structure. Theinvention can be suitably used in medical application for diagnosing thecancer cases of mammary glands at an early stage of a disease.

PRIOR ART

The known mammography devices are generally based on the principle thatdifferent substances, being subjected to raying, exhibit differentproperties of absorbing the X-ray radiation. The intensity of aradiation passed through an object and forming its projection image isdetermined by absorption property (absorption coefficient) of thesubstances constituting the object and by their thickness in the rayingdirection. To provide a quality image, it is necessary that a wholeobject would have the same thickness in the raying direction. The knowndevices provide said feature by compressing mammary gland to desired (orallowable) size (U.S. Pat. No. 4,962,515, Sep. 10, 1996). However, suchcompression results in that a patient feels a pain and discomfort.

Another method of compensating a variable thickness of an objectconsists in placing mammary gland in a cylindrical vessel filled with animmersion liquid that has the same X-ray absorption coefficient as thegland. Such approach is used, for example, in mammary gland tomography(U.S. Pat. No. 3,973,126, Mar. 08, 1976). For producing one projectionof mammary gland, a similar result can be attained by introducingplate-shaped attenuating filters (made of aluminium or other material)into the raying zone, in particular in cases of studying the subsurfacesubcutaneous areas of mammary gland (U.S. Pat. No. 4,969,174, Jun. 11,1990). There is no need of any compression in the use of this approachfor producing an image.

Another technique to obviate the need to compress mammary gland isprovided when an image is produced by scanning of an object with anarrow X-ray beam. In the device of such approach (U.S. Pat No.4,969,174, Jun. 11, 1990), an image is produced on a photographic film,under which film rows of X-ray detectors are arranged. The detectorsdetermine the time required for exposing the photographic film for eachof the raying beam position. A signal from the detector is supplied to ascanning system control unit, and allowance for various breast thicknesswas made for by different rates of the beam movement. In this system,scanning is performed along the breast axis.

In the devices based on principles of the conventional absorptionX-raying, i.e. on registration of intensity distribution of theradiation passed through a rayed object, the scattered radiation is aparasitic phenomenon that creates a background and affects the imagecontrast. To overcome the scattered radiation, said radiation isregistered separately using a collimating grid and a filter, and theregistered signal is deducted as the background from the total signalproduced when an object is rayed (U.S. Pat. No. 4,651,002). Thescattering pattern is measured integrally, and a filter is implementedas a movable member, the scattered radiation being measured at largeangles.

An essential index of performance of an X-ray mammography device is theirradiation dose absorbed by a patient during checking. A partialdecrease of the irradiation dose is provided by a decreased thickness ofthe checked object (breast compression).

Another technique to reduce the irradiation dose is selection of theX-ray radiation parameters. For example, application of replaceablefilters allows to select the radiation hardness for each patient (U.S.Pat. No. 4,969,174, Jun. 11, 1990).

When a patient's breast is scanned by an X-ray beam, the irradiationdose is decreased by monitoring of the passed radiation by detectors.Then the breast raying (scanning) is selected to be optimal so that tominimize the patient irradiation dose and produce a clear image.

In all above-discussed devices, a patient usually is positioned in thestanding or inclined position, and mammary gland is fixed normally tothe patient's body.

All above-discussed devices are based on the principle of producingimages as the difference in absorption of the rays passing through apatient's mammary gland via different paths. As coefficients ofabsorption by the breast soft tissues have only a slight difference, soit is difficult to determine minor changes in tissues in early stages ofa disease.

The mentioned drawbacks are avoided by using a method of registering theradiation coherently scattered by an object for producing an image. U.S.Pat. No. 4,751,722, G 01 N 23/22, 1988, describes a device, wherein theradiation passed through an object and the angular distribution of thecoherently scattered radiation lying at angles of 1° to 12° in relationto the incident beam direction are registered simultaneously. As saidpatent discloses, the main portion of the elastically-scatteredradiation is concentrated in the angles less than 12°, and the scatteredradiation has a characteristic angular relationship having pronouncedmaxima, the location of which maxima is determined both by theirradiated substance itself and the incident radiation energy. Asdistribution of intensity of the coherently scattered radiation withinsmall angles depends on the molecular structure of a substance, thendifferent substances having the same absorptive capacity may differregarding the distribution of intensity of the coherent radiationangular scattering being intrinsic to each substance. In case an objectis heterogeneous, i.e. consists of different substances, then intensityof a radiation scattered at each particular angle is constituted byintensities of the rays scattered by different substances on the path ofpropagation of a penetrating radiation beam. This patent proposes to usea narrow collimated beam of a monochromatic or polychromatic radiationfor irradiating an object. A detecting system has the resolutionproperty both for energy and coordinate (scattering angle). Said devicecomprises an X-ray source having a diaphragm that forms a primaryradiation beam such that said beam has a small cross-section in theplane normal to the beam propagation direction. Having passed through atested object, the beam is registered by a row of detectors, one ofwhich is positioned such that it registers the primary beam passedthrough an object (or the tested object area), the other detectors beingpositioned in the plane normal to the ray plane, or on a straight linein said plane, and oriented such that they register only the coherentlyscattered radiation. Further, each detector of said detector rowregisters the radiation that is scattered at a certain angle.

The above-described device has a relatively low sensitivity to theradiation scattered in immediate vicinity of the primary beam, becausethe primary beam radiation intensity considerably exceeds that of thescattered radiation and hinders the registration thereof. Further, theradiation intensity sharply falls when the scattering angle grows, thusthe coherently scattered radiation intensity within the range of 1-12degrees is low, hence the sufficiently high irradiation doses and a longexposure are required for testing an object.

DISCLOSURE OF THE INVENTION

The object of the invention is to provide devices that are moresensitive to registration of the coherent scattered radiation inultra-small angles (tens of seconds to one degree), which will allow toreduce the radiation dose in testing of an object. Attainment of saidobject will allow to avoid compression of breast, i.e. avoid patient'spain and discomfort.

The main part of coherently scattered radiation is concentrated in thecentral diffraction peak that is situated in the scattering angles of 0to 1 degree relative to the primary beam incidence direction. In thisangular range concentrated is the radiation coherently scattered byheterogeneities of the object electronic structure, whichheterogeneities have characteristic dimensions of several hundreds totens thousands Angstrom, which corresponds to structure of manybiological objects. This is the reason to measure distribution ofcoherently scattered radiation just within this angular interval. Themeasurement angular range depends on wavelength of the used radiationand structural properties of a material, and can be within the range ofseveral angular seconds to 1 degree relative to the incident beam. Theinvention proposes to use the dark-field measurement technique, where inthe absence of a tested object a detector registers only the backgroundsignal, and when said object is present it registers only the scatteredradiation.

For producing an image representing distribution of the tissuestructural characteristics in an object, the invention proposesdifferent embodiments of mammography devices that provide registrationof the radiation angular distribution in said angular interval, or thatof the radiation integral intensity within the angular interval of oneangular second to 0.5 degree; as well as simultaneous registration ofthe radiation passed through a tested object. In reference to the natureof the scattered radiation angular distribution curve and a value of theintegral signal of the coherently scattered radiation in said angularinterval, the structure of a tested object can be ascertained.

The first embodiment of the device that achieves the above-statedobject, is a device intended for reduced-angle mammography, comprising asource of a penetrating radiation, collimator that forms a radiant fluxincident upon an object in the form of narrow small-divergencefan-shaped beams (or a beam), a spatial filter disposed downstream ofthe object and a position-sensitive detector. The spatial filter ispositioned to overlap the radiation primary beam and provide passing ofthe coherent radiation scattered in ultra-small angles near the primarybeam boundaries, to a detector. The proposed system that consists of asource, collimator, spatial filter, detector, is fitted to a framecapable of moving relative to a tested object in the plane normal to thebeam plane. The frame is adapted to rotate with respect to the objectaxis to ray the same from different directions. In some cases, thepossibility to move a patient relative to a fixed frame is provided for.

In the second embodiment of the device: a frame having a source,collimator, spatial filter and detector is capable of swinging about anobject in the plane normal to the beam plane for the purpose to scan theobject.

The third embodiment of the device is also proposed, wherein itcomprises at least another radiation source having a collimator, spatialfilter, position-sensitive detector which are identical to the firstones. In this embodiment, each system, consisting of a source,collimator, spatial filter, detector, is capable of moving one afteranother, opposite to one another and in two mutually perpendiculardirections in the plane normal to the beam plane.

In any of the proposed embodiments, a collimator can be implemented inthe form of one slit or in the form of a regular periodic structurebeing the radiation-transparent areas in the form of slits, and theopaque areas interleaved therewith. Use of a multi-slit collimator thatforms a number of small-divergence beams allows a more efficient use ofthe source radiation. The rays formed by the collimator overlap aseparate strip in the object projection. The spatial filter in this caseis a collimator-like regular periodic structure, wherein the areascorresponding to the collimator transparent areas are made of a materialopaque to a penetrating radiation such that the filter opaque areasoverlap the collimator transparent areas. Further, size of slits, andstructural period of the collimator, and size of transparent areas ofthe spatial filter must provide registration of only the radiationcoherently scattered at small angles by the position-sensitive detector.The collimator must form the beams having a width and divergenceproviding the possibility to register the radiation scattered within asmall-angle range, i.e. so that any ray scattered by an object at asmall angle will transgress the primary beam boundaries in theregistration zone. Further, the structural period of the collimator mustby such that adjacent beams will not overlap one another in the detectorplane. To register the source's primary radiation that passed through anobject, additional elements of the position-sensitive detector arepositioned on the filter opaque areas.

In any of the proposed embodiments, a translucent spatial filter thatoverlaps the radiation primary beam passed through an object and reducesits intensity at least to the level of the scattered radiation intensitypreferably less than a number of times, can be used also. This willallow to improve sensitivity to the radiation scattered in immediatevicinity of the primary beam and, consequently, further reduce thepatient irradiation dose.

For the purpose of a more substantial decrease of the patientirradiation dose and to make the exposure period briefer, thepossibility to register the scattered radiation integral flux in aparticular angular range is also provided; the highest contrast of animage (contrast is obtained by a difference in the integral intensity ofthe radiation scattered by each of the irradiated substances) is to beachieved in registration of the coherently scattered radiation withinthe angular interval of several seconds to 0.5 degree. Changes in thesignal level relative to the whole flux of the coherently scatteredradiation will be determined by the scattering function of a givenobject. In this case it is preferable to use one-coodinateposition-sensitive detectors implemented as linear gas meters, andregister the scattered radiation in the quantum counting mode.

An improvement of sensitivity to the radiation scattered in immediatevicinity of the primary beam can be attained by forming a beam having asharp boundary and by an high precision of positioning of the spatialfilter with respect to the collimator. For achieving this result, in thedevice, the collimator and spatial filter are implemented as a singleunit whose entry portion facing the radiation source is a Kratkycollimator having input and output diaphragms. The upper edge of theinput diaphragm is situated in the plane that is common with the netheredge of the output diaphragm and the upper edge of the spatial filter; afree space is provided between the collimator and spatial filter, whichspace is intended for movement of an object.

An X-ray source having radiation hardness and intensity that provide aminimal patient irradiation dose, while producing a quality image, isselected as the source. Size of the radiation source focal spot dependson the <<collimator-spatial filter>> system used in a particular device.The <<collimator-spatial filter>> elements are interrelated anddetermine all operation parameters of the proposed device.

An example of design of a device based on the described principle andits basic parameters is given below.

The device includes: an X-ray source, collimator (or a unit ofcollimators), patient table equipped with a system of relative movementof the device and patient, spatial filter and position-sensitivedetector; and also a system of registration, analysis and imaging ofdata, and a system of adjusting the device and monitoring itsparameters. The devices allows to produce an image of a tested object inthe rays scattered at small angles, spatial resolution of details of anobject being about 100 μm. The intended contrast in such arrangementmust 1.5-4 times exceed that obtained in conventional mammography imagesproduced by different absorptivity of X-ray radiation by an object.Total analysis time does not exceed 1 min. The dose absorbed by apatient during the whole testing time will not be over 4 mGy. Below aregiven parameters of the device elements that permit to achieve theseresults.

X-ray Source

Used is a standard source of pulse X-ray radiation, having a rotatingmolybdenum anode. Voltage across the X-ray tube is selected within therange of 20-40 kV, the pitch being 0.5 kV, depending of the testedobject parameters. Value of current in such arrangement is 16 to 120 mA.Size of the source focal spot is 0.3×0.3 mm. The distance from thesource focal spot to the collimator input is 100 mm.

Collimator

The used collimator is implemented as a Kratky collimator. Height of thecollimator input slit is 80 μm, length being 85 mm. Total length of thecollimator is 100 mm. The collimator forms a narrow fan-shaped X-raybeam having at least one sharp boundary. Size of the X-ray beam in theobject plane is 0.1×180 mm.

Spatial Filter

The spatial filter must be implemented of a material that well absorbsand weakly scatters the X-ray radiation. The distance from a testedobject to the spatial filter is 500 mm. The plate of which the spatialfilter is implemented must have extremely even working edges across theentire width of the X-ray beam.

Space-Sensitive Detector

The space-sensitive detector is a two-dimension array of the elementssensitive to X-ray radiation, for example a CCD-array. The detector isto be positioned immediately downstream of the spatial filter.Dimensions of the space-sensitive detector: 5×420 mm, size of pixelsbeing 100 μm. Such arrangement will provide registration of distributionof intensity of the scattered radiation with angular resolution of 40angular seconds.

BRIEF DESCRIPTION OF DRAWINGS

The invention essence is explained by drawings, in which

FIG. 1 shows an embodiment of a mammograph, wherein the system,consisting of a source, collimator, spatial filter, detector, is adaptedto move relative to an object in the plane normal to the beam plane, andalso rotate relative to the object while being fixed in each position sothat to ray a selected area of an object at different angles;

FIG. 2 shows the second embodiment of the device, wherein said system isadapted to rotate about an object in the plane normal to the beam plane;

FIG. 3 shows a device having two identical sources with collimators and,respectively, with two filters and position-sensitive detectors;

FIG. 4 shows a device that provides for movement of a patient relativeto the system, consisting of a source, collimator, spatial filter,detector, wherein an integral detector is used as a detector forregistration of the scattered radiation, which integral detectorcollects the whole scattered radiation within a predetermined angularinterval;

FIG. 5 shows distribution of intensity of the coherently scatteredradiation by different tissues of mammary gland;

FIG. 6 shows a possible implementation of a portion of the device, whichportion is intended for forming a beam of radiation that rays an object,and for extracting the radiation scattered by an object, in accordancewith the invention.

EMBODIMENTS OF THE INVENTION

Devices are operated as follows. Radiation from source 1 of apenetrating radiation, for example, X-ray tube, is formed usingcollimator 2 into planar fan-shaped beam 3 (FIG. 1), or a number offan-shaped beams (as in FIG. 2), and is directed to tested object 4disposed on holder 5. On the path of the passed 6 through the object andscattered 7 radiation, positioned is position-sensitive detector 8 inthe form of an array of radiation-sensitive elements intended forregistration of the reduced-angle scattering, and also radiation-opaquefilter 9 whereon positioned is detector 10 for registration of theradiation passed through the object. The registration system can bearranged in another way: filter 9 can be translucent, detector 10 can bedisposed downstream of the filter. All instruments intended to form theradiation field and perform registration are disposed on frame 11installed in turn on base 12. The frame on guides is moved in thedirection normal to the radiation beam plane to scan the object, and thebase is adapted to rotate as being fixed at each setting so that toprovide irradiation of the tested object at various angles.

FIG. 2 shows the embodiment of the proposed device wherein frame 11 isadapted to swing relative to the object in the arrowed directionrelative to the axis extending through the source focal spot. In thisembodiment: 2 is a multi-slit collimator that forms several fan-shapedbeams 3. Filter 9 that overlaps the radiation primary beam, passedthrough the object, consists of identical areas, number of which areasis equal to that of the collimator slits, and can be implemented asbeing translucent to the incident radiation. Then portion 8′ ofdetectors 8 of the detector array, positioned downstream of the filters,registers the radiation passed through the object and attenuated to thescattered radiation level, and remaining portion 8″ of the detectorsregisters the radiation scattered at small angles. Filter 9 can also beopaque. In this case, upstream of the filter (or thereon) positioned aredetectors that register the primary beam that passed through the object,as shown in FIG. 1.

FIG. 3 shows the third embodiment of the device. An object is rayed withtwo penetrating radiation sources 1 and 13. Collimators 2 and 14 formtwo fan-shaped beams to irradiate the object. Translucent filters 9 and16 reduce intensity of the radiation passed through the object to amagnitude of the same order as the scattered radiation. Two arrays ofdetectors 8 and 15 register the entire radiation downstream of theobject; a portion of the detector elements, that is disposed in theprimary beam downstream of the translucent filter, measures the passedradiation, and the remaining portion of the detector elements measuresthe reduced-angle radiation coherently scattered at respective angles.The registered signals are supplied to information processing unit 17.Each of the system, consisting of a source, collimator, spatial filter,detector, is arranged on frames 18 and 19, respectively, adapted to moveone after another in the plane normal to that of radiation beams 3 and20.

FIG. 4 shows the device wherein a patient is moved relative to base 21,whereon positioned are source 1 with collimator 2, spatial filter 9 anddetector 22. Space-sensitive detector 22 is a one-coordinate lineardetector having resolution along the beam 3 plane. This device usesopaque filter 9, whereon positioned is detector 10 that registersintensity of the radiation passed through the object. Table 23, whereona patient is to be positioned, is equipped with means for movementrelative to base 21 in the plane normal to the beam 3 plane.

FIG. 5 shows difference of scattering properties of the healthy tissueof mammary gland and that of a cancer tumour. The scattering function ofany substance is determined by its structure and is the <<identitycard>> of a given substance and its condition, and can be used toidentify them. Thus, by comparing the measured distribution of intensityof the reduced-angle coherently scattered radiation and the integralvalue of intensity of the radiation scattered within a specific angularrange with the results stored in a database for the control objects, aparticular tissue that has a scattering property resulting in suchangular distribution can be determined. FIG. 5a shows the curve ofdistribution of intensity of reduced-angle scattering of radiation,which scattering is effected by the cancer tumour tissue, and FIG.5shows that of the adjacent unaffected tissue of mammary gland.

FIG. 6 shows a portion of the device, which portion, in any of theembodiments, allows to form a beam of radiation that rays an object andto extract the radiation scattered by the object. This portion of thedevice is implemented in the form of frame 24, in which frame space 25is intended for accommodating tested object 4. The upper portion ofcollimator 2 is implemented as unit 26 having stepped cuts that forminput 27 and output 28 diaphragms, which diaphragms form a fan-shapedbeam having a sharp upper boundary (Kratky collimator). Depending on thetesting purpose, number of diaphragms can be increased. The upperboundary of filter 9 is situated in the plane that is common with theupper boundary of output diaphragm 28 so that only the radiationscattered by the object would fall on the detector.

What is claimed is:
 1. A mammography device, comprising a source of apenetrating radiation having a slit collimator, holder of a testedobject and position-sensitive detector with an information processingsystem, characterised in that the detector is provided with a spatialfilter designed to extract, on the detector, a reduced-angle coherentlyscattered radiation, the source with the collimator and the detectorwith the filter being positioned on a frame, the device being providedwith means for relative movement of the frame and object in the planenormal to that of the radiation beam, and for discrete rotation of theframe with fixing of the same in each position relative to the testedobject holder.
 2. The device as claimed in claim 1, characterised inthat the collimator is implemented as a multi-slit collimator, and thespatial filter is implemented in the form of a periodic structure,comprising areas transparent and opaque to radiation, the filter opaqueareas carrying elements of the space-sensitive detector intended toregister the primary beam of the radiation passed through the object. 3.The device as claimed in claim 1, characterised in that the spatialfilter is translucent to the incident radiation.
 4. The device asclaimed in claim 3, characterised in that the position-sensitivedetector is an one-coordinate detector in the form of a linear gasmeter.
 5. The device as claimed in claim 1, characterised in that thecollimator and spatial filter are implemented as a single unit whoseentry portion facing the radiation source is a Kratky collimator havinginput and output diaphragms made in the form of stepped cuts in the unitbody; the upper edge of the filter being situated in the plane that iscommon with the upper edge of the collimator output diaphragm, andbetween the collimator and filter free space to accommodate an objectbeing provided.
 6. A mammography device, comprising a source of apenetrating radiation having a slit collimator, holder of a testedobject and position-sensitive detector with an information processingsystem, characterised in that the detector is provided with a spatialfilter intended to extract, on the detector, a reduced-angle scatteredradiation, the source with the collimator and the detector with thefilter being positioned on a frame provided with means for swingingrelative to object holder in the plane normal to that of the radiationbeam.
 7. A mammography device, comprising a source of a penetratingradiation having a slit collimator, holder of a tested object andposition-sensitive detector with an information processing system,characterised in being provided with at least one additional pair of thesource with the collimator and the position-sensitive detector, eachdetector being provided with a spatial filter intended to extract, onthe detector, a reduced-angle scattered radiation, each pair beingpositioned on a frame designed to provide the possibility of movementone after another, toward one another and in two mutually perpendiculardirections in the plane normal to that of the radiation beam.